The invention relates generally to a mowing apparatus of the reciprocating sickle type and more particularly to the means for maintaining the sickle in a stabilized, efficient and proper shearing relationship with the underlying sickle guards.
Crop harvesters for mowing apparatus generally include a reciprocating sickle provided with triangular-shaped knife sections and suitable stationary sickle guards which are typically slotted to accommodate a horizontally moving sickle. The guards serve a dual purpose of protecting the sickle from damage and breakage from rocks or other hard objects encountered in the field and of providing a co-acting shear surface to assure a scissor-like action in cooperation with the reciprocating sickle.
The greatest of problems has been in maintaining the cutter sections of the sickle in a sliding relationship to the underlying sickle guards so as to assure an efficient shearing action in cooperation with the ledger plates on the sickle guards. It is important for the optimal operation of the sickle to maintain the sickle bar knife substantially parallel to the ledger surface of the guards and to maintain proper clearance between them for good shearing action.
The knife sections are subjected to irregular but significant upward forces as the sickle and ledger surface of the guard encounter and sever plant material. Heavy grasses and crops, dirt, rocks and other objects tend to clog the cutter assembly and cause the sickle to lift off the guards. If such deflections and upward movement is too great, the proper cooperative shearing action between the sickle knife and the guard ledger surface will be lost. Plant material and debris will either hairpin over the edges of the ledger surface or lodge into the gap between the knife and ledger surface instead of being severed in the intended manner. The deflection of the sickle causes excessive wear through friction of the blade which results in breakage of the sickle or guard portions. Damaged or broken sickle blades require replacement which is often a tedious and time consuming operation.
It has been found necessary to provide some type of hold down plate or clip to retain the sickle in place. The hold down plate or clip helps maintain a proper clearance between the sickle and cutting surface of the guards and resists the upward deflection of the sickle. To maintain the proper clearance between the sickle knife and cutting surface, adjustment means are typically provided on the hold down clip. The difficulty and inconvenience of adjusting hold down clips often results in mowers being operated with improper knife clearance. Too much clearance allows plant material to force the knife blade away from the cutting surfaces and edges of the sickle guard, thereby reducing cutting efficiency. Too small a clearance results in drag on the sickle and an increase in the wear on the sickle and the power required to move the sickle.
Attempts at providing hold down clips with adjustment means have included designs with mounting bolts which must first be loosened before an adjusting screw can be turned to provide for greater or lesser clearance between the sickle and cutting surface such as illustrated in U.S. Pat. No. 4,894,979 to Lohrentz. After the desired adjustment is made, the mounting bolts need to be retightened to return the apparatus into operating condition. This design requires a two step procedure to attain the desired adjustment and entails possible loosening of other components of the cutter assembly such as the guards and wear plates of the sickle bar assembly.
Some designs utilize a multipiece design with a two nut or two screw adjustment means for maintaining a hold down plate in spaced relation to the sickle blade such as illustrated U.S. Pat. No. 4,012,891.
Other solutions such as disclosed in U.S. Pat. No. 4,553,380 to O'Halloran, utilize a fully enclosing sickle guard which is adjusted to vary the slot between the sickle and retaining sickle guards through which the sickle reciprocates. Such designs do not rely on a wear pad in loaded tension to vary the slot.
Other attempts utilize a hold down clip with constant pressure on the knife sections. This clip is in constant contact with the sickle, thereby imparting a drag on the sickle with increased wear and increased power requirements.
In another design, such as the hold down clip illustrated in U.S. Pat. No. 3,455,0932 to Stern, a loaded spring causes a clip to swing about a hinge pin until a rub strip engages the upper surface of the sickle blade. A nut can be adjusted to adjust the pressure exerted on the sickle blade by the rub strip. A pressure release member is used to separate the rub strip from the sickle blade. One embodiment of applicant's invention also utilizes a loaded spring and a nut adjustment means. Applicant's invention, however, discloses a loaded tensioning spring which lifts the clip and pad away from the sickle blade rather than toward it. Adjustment or contact with the sickle blade is made through a nut which counteracts the lifting action on the clip. No extra pressure release member is needed to remove the hold down clip off the sickle blade. The lifting action of the clip is facilitated by a pivot member located at the rear of the clip so that the tensioning means is between the pivot member and the contact point of the clip with the sickle. By contrast, in Stern a centrally placed horizontal hinge pin is located between the tensioning means and the contact point of the clip with the sickle.
The present invention in a preferred embodiment also provides for a base plate which further acts as a stabilizing device on the sickle. Furthermore, the present invention discloses wear pads which may be specially heat treated in contrast to the antifriction rub strip disclosed by Stern. Applicant's hold down clip also consists of a minimum of parts allowing simplified manufacture.